We integrate previous Bayesian and astronomically tuned age calibrations of the calcareous nannofossils events with our large-scale correlations to discuss using the standard calcareous nannofossil zonal schemes in the SW Neo-Tethys platform during a period of significant paleoceanographic, tectonic, and paleoclimatic perturbations (middle Eocene to early Oligocene). Two marine on-land sections extend from NP15 (Nanno-Plankton zone) to lower NP23, equivalent to upper CNE9 (Calcareous Nannofossil of the Eocene) to lower CNO3 (Calcareous Nannofossil of the Oligocene), are studied. Calcareous nannofossils have been investigated at less than 96 kyr resolution between 45.55 Ma and 31.9 Ma. The Souar section covers the Top (T) of the Nannotetrina alata group zone (CNE9, Lutetian) to the Isthmolithus recurvus zone (CNE18, Priabonian) in the Pelagic facies of the Tunisian dorsal. The El Rahma section extends from the Helicosphaera compacta zone (CNE21) to the Reticulofenestra umbilicus (CNO2) zone in the Cap Bon peninsula. The distribution patterns were studied through semi-quantitative counts to test the reliability of the biohorizons used in the standard biozonations schemes (Martini, 1971; Agnini et al., 2014). We discuss 14 biohorizons that span 13.65 Myr to highlight the limitations (absence/scarcity) of the Chiasmolithus group, particularly Ch. grandis, Ch. oamaruensis, and Ch. solitus, as biohorizons in the SW Neo-Tethys. Our study shows that Sphenolithus furcatolithoides, Dictyococcites bisectus, Sphenolithus obtusus, and Reticulofenestra erbae are reliable horizons for large-scale correlations with the northern margins of the Neo-Tethys. Calcareous nannofossils from the SW Neo-Tethys margin were highly affected by the paleo-circulation changes due to the episodic restriction of the westward subtropical Eocene Neo-Tethys (STENT) current (Jovane et al., 2009), followed by the closure of the eastern Neo-Tethys.